Non-P car brake question

drcoastline · 09-01-2017, 12:04 PM

I received a brake kit for my DD. Four rotors and pads. It seems the tolerances are a few MM's to thick all the way around. Rotors and pads. What if any issue is there if I were to sand a few MM's off each pad with say 400? Returning them under warranty will cause the vehicle to be inoperable for at least five days.

rwest · rwest's Garage

Just a thought, because it happened to me. Seemed like either the pads or rotors were too thick, turned out that being single piston caliper with rusted slide bolts wasn't allowing it to center making me think things were oversized.

fanaudical · fanaudical's Garage

Sorry to ask, but are you sure you have the calipers pistons retracted enough?

drcoastline · 09-01-2017, 12:57 PM

Quote:

Originally Posted by rwest

Just a thought, because it happened to me. Seemed like either the pads or rotors were too thick, turned out that being single piston caliper with rusted slide bolts wasn't allowing it to center making me think things were oversized.

I checked that. Lower slides are hanging up but I can get the to move. I measured all the calipers and pads. Calipers are all about .25 over size. Left front had a stone get caught between the pad and rotor causing damage. Scored the rotor and chewed up the pad, which is what prompted me to buy the new kit. As a temporary fix I bought a cheap set of pads which came with both sets. I threw one set on. Didn't install the other. I measure the unused set against the kit set. Kit is also a few MM's over.

Rears go on but need lots of persuasion. Fronts not at all. I did put the unused set in the calipers and it went right on.

So I am think if I can slim these kits down a bit they will go one. I just don't want to do any damage.

Bob Kontak · Bob Kontak's Garage

Quote:

Originally Posted by rwest

Just a thought, because it happened to me. Seemed like either the pads or rotors were too thick, turned out that being single piston caliper with rusted slide bolts wasn't allowing it to center making me think things were oversized.

Probably not going to happen on all four corners.

Forget 400 grit. Kiss your weekend goodbye.

Get an angle grinder if you must drive the car now. Dress the face of the pads like you are an artist. The car will do the rest. Make sure all sliders and pad mounting points are functional. Pads must fit in their mounting points nicely and not be bound up.

YOU drive the car until you are satisfied there is sufficient braking. Stink them up a couple of times. You will not get 100% pad/rotor interface for several months.

This is totally back woods engineering and no one can say it's the thing to do. Just talking because if mail order is what you did, you paid peanuts for the pads so chew them up.

javadog · 09-01-2017, 01:56 PM

If the parts are that far off they are probably of poor quality and I wouldn't put them on my car at all. Reputable companies don't make mistakes like that. If you have to keep the crap, take the pads to a machine shop and have them machined to a lesser thickness. If you end up sanding them yourself, it'll take you the rest of your life and when you get done they won't be flat and parallel.

Cal44 · Cal44's Garage

this is very common. From P cars to early Lotus Elans and '70 Boss 302's. I use a fine file and take my time then finish on the side of the electric stationary grinding wheel. I reckon I'm a hillbilly but it works every time.

fastfredracing · 09-01-2017, 02:04 PM

With the pad mounted in a vise, a belt sander makes quick work of the pad face . Wear a mask.

drcoastline · 09-01-2017, 03:41 PM

Thanks all, this is what I wanted to know. It's not much but enough that they don't go in. After Bob's post I was going to use a belt sander. Fred cinched it for me. I was looking to keep the faces nice and fine. So I guess 80 would work?

sc_rufctr · 09-01-2017, 06:40 PM

Quote:

Originally Posted by fanaudical

Sorry to ask, but are you sure you have the calipers pistons retracted enough?

OP Did you check this?

pen15 · pen15's Garage

Your slides are stuck. Remove fully from caliper hanger, clean, lubricate, and reinstall. They must move free. I have never seen pads that are too thick. There is always plenty of extra space. Do not grind or sand the pads. They contain asbestos even today.

drcoastline · 09-02-2017, 02:45 AM

Yes, Pistons are retracted fully. Past the Caliper housing.

Slides are operable. Slides on back brakes move freely. Upper slides on fronts move freely. Lowers are stiff but move.

fastfredracing · 09-02-2017, 03:29 AM

I have ran into to this before . I was working on an Aveo, and there was no combination of pads and rotors that would fit.
Customer with no money, and of course in a hurry. Tried oem, and aftermarket . After a day of dickering around, I finally gave up , and shaved a few thousandths off the pads .

drcoastline · 05:15 AM

Thanks Fred,

I am just going to shave a bit off. I just wanted reassurance I wouldn't damage the rotors if there were any imperfections in the pad face.

So this whole thing started because the front driver side had a pulsing feel during braking. It gradually has gotten worse. I assume it is a warped rotor. Which it may be, I don't know. A little over a year ago I had an accident on this side and the upper control arm snapped from the collision. It's possible this was damaged at that time but not picked up? I don't know that either. Last week The pulsing got real bad under braking and began to grind. So I inspected the problem and found that the inside pad was coming apart and had a stone embedded. In addition the inside surface of the rotor was severely scored. The other three brakes were fine but I decided to replace rotors and pads on all four corners.

OEM front rotor thickness specs are 30mm max thickness. The set I received is 30.25mm. So slightly over. Everything else seems ok. As I posted above I purchased a cheap set of front pads from AutoZone to use until the kit came in. I only installed one set of pads on the front left. Yesterday I compared the unused pads from that set to the pads in the kit.

Unused pads measure 12.06, 12.07 MM

Kit pads were 12.09, 12.26, 12.28, 12.28 MM.

Rears were a tight fit but went on. For now I put the unused AutoZone pads on the front right and the old front right on the left.

javadog · 06:28 AM

It's unlikely that you will damage the new rotors with a set of pads that you have sanded to a thinner thickness. What is more likely is that you will probably not sand them evenly, which is very difficult to do by hand, and you'll end up with less than perfect contact between the pads and the rotors initially. It has the same effect as taper wear on the pads.

I'm not a huge fan of mixing pads of different brands or types, either front to rear or on the same axle. You don't know what the friction coefficient of the pads might be and you can upset the basic mechanical balance of the braking system if they differ in a substantial way. It's not a big deal nowadays, given the near universal application of ABS, but it's still not ideal. It's not something you would really be bothered by if you're just poodling around town at low speeds, but I don't know what type of car we're talking about here or how you use it.

It's possible that the old rotor, or maybe more likely the hub on that side, could have been damaged in the crash. It's definitely something I would check. Warped rotors are probably less of a likelihood than instances of uneven pad deposition on the rotors, unless the rotors that we're run previously were of really poor quality.

drcoastline · 09-02-2017, 06:03 AM

Quote:

Originally Posted by javadog

It's unlikely that you will damage the new rotors with a set of pads that you have sanded to a thinner thickness. What is more likely is that you will probably not sand them evenly, which is very difficult to do by hand, and you'll end up with less than perfect contact between the pads and the rotors initially. It has the same effect as taper wear on the pads.

I'm not a huge fan of mixing pads of different brands or types, either front to rear or on the same axle. You don't know what the friction coefficient of the pads might be and you can upset the basic mechanical balance of the braking system if they differ in a substantial way. It's not a big deal nowadays, given the near universal application of ABS, but it's still not ideal. It's not something you would really be bothered by if you're just poodling around town at low speeds, but I don't know what type of car we're talking about here or how you use it.

It's possible that the old rotor, or maybe more likely the hub on that side, could have been damaged in the crash. It's definitely something I would check. Warped rotors are probably less of a likelihood than instances of uneven pad deposition on the rotors, unless the rotors the runner previously were of really poor quality.

Thanks Javadog,

The vehicle is a Jeep Commander. It's used to commute and isn't driven hard but I do drive on the highway. It's an '06 and I just broke 100K. My intent is to have all four pads match. Rears currently match and are from the kit. Fronts do not at the moment but I will swap out hopefully today. I am going to sand on a belt sander as FF suggested, hopefully this will keep them relatively flat. Old rotors were original.

Scott Douglas · Scott Douglas's Garage

If you have a vertical belt sander with a table, you could try clamping the pads to a machinist's knee to help keep the surface sq.

Bob Kontak · Bob Kontak's Garage

Quote:

Originally Posted by javadog

Warped rotors are probably less of a likelihood than instances of uneven pad deposition on the rotors, unless the rotors that we're run previously were of really poor quality.

I have run across two sets of warped rotors recently. Rare.

One was from a truck that pulled a boat and the owner said it had happened to him previously. Suspect poor trailer braking and/or driving habits.

The other set was brand new on an old Camry. Weeks old. 0.020" out of parallel. Cheapest ones he could buy on ******** (edit:mail order). Had them turned.